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Re: Re: [COMMITTERS] pgsql: Rewrite GEQO's gimme_tree function so that it always finds a

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: marcin mank <marcin(dot)mank(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: [COMMITTERS] pgsql: Rewrite GEQO's gimme_tree function so that it always finds a
Date: 2009-11-28 01:32:32
Message-ID: 2407.1259371952@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
marcin mank <marcin(dot)mank(at)gmail(dot)com> writes:
> This is pretty off-topic, but if we had some upper bound on the cost
> of the complete plan, we could discard pieces of the plan that already
> cost more.

> One way to get the upper bound is to generate the plan in depth-first
> fashion, instead of the current breadth-first. Instead of bottom-up
> dynamic programming, employ memoization.

Well, the breadth-first approach also allows elimination of large parts
of the search space.  It's not immediately obvious to me that the above
would be better.  You should be able to try it if you want though ---
these days, there's even a hook to allow replacement of the join search
strategy at runtime.

			regards, tom lane

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